The hypothesis that guides this project is that trigeminal nerve axotomy results in: (i) the degeneration or atrophy of selective trigeminal ganglion cell populations, and (ii) transganglionic degeneration of second-order neurons within the spinal trigeminal and main sensory nucleus. Furthermore, repair by epineurial reanastomosis results in: (i) regeneration of selective trigeminal ganglion cell populations, and (ii) enhances the process of transganglionic regeneration that normally follows central degeneration within the spinal trigeminal and main sensory nucleus. The proposed studies seek to carefully evaluate the anatomical events of trigeminal axotomy and the consequences of early versus delayed direct repair. In general, we propose to carry out a detailed evaluation of existing cell populations in the trigeminal ganglion after peripheral axotomy and early of delayed (months) repair by using staggered double-fluorescence labeling methods in rats. The presence of double-labeling and the morphometric characteristics of existing trigeminal ganglion cells will be compared with those obtained from control (sham and axotomy-without-repair operated) rats. In a parallel study, the same rats (axotomy with early and delayed repair and controls) will be evaluated for the presence of transganglionic degeneration (using a genuine marker for transganglionic regulation of sensory neurons) within the spinal trigeminal and main sensory nucleus. It is anticipated that the evaluation for double-labeling and morphometric change of ganglion cells, and detailed observance of transganglionic regulation after injury and repair of the trigeminal nerve will: (i) determine if, and to what extent, selective cell degeneration occurs in the ganglion after peripheral axotomy; (ii) more clearly resolve the question of whether nerve repair results in the reconnection of ganglion cells; (iii) characterize the effects of peripheral nerve injury and repair on second-order neurons and, finally (iv) enable finer stratification of guidelines for peripheral nerve repair. The methodologies and anticipated results, if verified by these studies, should provide the foundation for a more expanded project to examine the effects of therapeutic interventions intended to alleviate the pain and discomfort associated with peripheral nerve injury in the orofacial region.